Bt-corn is a transgenic corn modified to express the cry1Ab gene from the soil bacterium Bacillus thuringiensis. It was tested in open field experiments in Egypt between 2002 and 2007. The investigation aimed at assessing the impacts of the genetically modified corn on: (i) biological efficacy against three species of corn borers, Sesamia cretica Led., the purple-lined corn borer Chilo agamemnon Bles. (ii) yield and yield components (iii) effect on non target insects (iv) development of borer strains resistant to cry1Ab gene. The results of the efficacy investigation advocate that S. cretica and C. agamemnon were more deleterious to non-Bt plants. The infestations of S. cretica, C. agamemnon and O. nubilalis were negligible or completely prevented in Bt hybrids (two yellow endosperm and one white endosperm) throughout the whole season and for three sowing dates. The range of infestation reduction was 90.48-100% for Bt hybrids. When reduction was below 100%, a few failed infestations were appeared. This study points to the potential agronomic and environmental benefits of Bt corn in Egyptian cropping systems. Insect resistance management strategy was investigated through surveying the dynamic of borers’ population on corn and alternative plants host species. The data support that alternative hosts can be used as functional refuge for diluting the probable development of insect strains resistant to cry1Ac. Common Reed , Broom Sorghum, Sweet Sorghum, Sugar cane, Rice and Barnyard Grass are specific hosts for S. cretica and/or C. agamemnon and/or O. nubilalis. The study revealed that few vegetable crops could act as alternative hosts for corn borers: cabbage is a host for C. agamemnon, potato, pepper and tomato are hosts for O. nubilalis. Cropping and intercropping of these alternative host species provide sufficient functional refuges for susceptible populations of borers which would mate with potential resistant strains that could arise in fields of Bt-corn.